Apparatus for and method of pulse keying



June 11, 1946. L woLFF APPARATUS FOR AND METHOD OF PULSE KEY ING Filed June 16, 19:59

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Irvzlzy Patented June 11, 1946 APPARATUS FOR AND METHOD OF PULSE KEYING Irving Wolff, Merchantville, N. J assignor to Radio Corporation of America, a corporation of Delaware Application June 16, 1939, Serial No. 279,542 12 Claims. (01. 250-17) This invention relates to apparatus for and the method of pulse keying. More specifically, the invention includes apparatus for creating and transmitting marking impulses of extremely short duration.

Numerous high speed mechanical keying systems have been devised for forming telegraphic characters. In general, these systems have been designed so that the keying prevents an abrupt interruption of the oscillatory currents because such abrupt change causes transient effects which interfere with reception. In general, the prior art keying devices attempt what is known as rounded keying.

The present invention does not involve the ordinary Morse keying, but relates to a keying system in which the pulses are of extremely short duration and in which no attempt is made to produce rounded keying. In fact, the present invention has for one of its objects the production of an extremely sharp, well defined keying pulse. Another object of the invention is to provide means for shortening a keying pulse beyond the limits'which re practical for oscillator keying. An additional object is to provide means for generating pulses of diminishing duration and applying one of the longer pulses to the oscillator and one of the shorter pulse to a power amplifier.

The invention will be described by reference to the accompanying drawing in which Figure 1 is a circuit diagram of one embodiment of the invention; and Figures 2 and 3 are graphs illustrating the operation of the invention.

In a copending application Serial No. 182,418, filed December 30, 1937, for Apparatus for and method of pulse keying, I have described a pulse keying device in which the pulses are first derived from a saw-tooth ,wave generator. The saw-tooth wave currents are stored in a capacitor which charges through a transformer. The transformer is coupled, to an amplifier which responds only to positive pulses. These positive pulses are differentiated by an inductor and are converted into highly damped wave trains. The positive pulses of these highly damped Wave trains are selected to be further amplified and converted into other high damped wave trains in which the positive pulses are of lesser duration than the original pulses. A portion of the final positive pulses is used to key an oscillator which is connected to an antenna. Radio frequency pulses radiated from the antenna are used to detect obstacles.

In view of the velocity of propagation of radio waves, it is necessary that the-outgoing pulse be extremel short to prevent its overlapping pulses reflected from a nearby object. With the system shown in the above mentioned copending application, it has been practical to generate radio frequency pulses having a direction as short as 1% of a micro-second and'at a frequency of the order of 500 megacycles.

In order to have an oscillator generate power with reasonable efiiciency, it should have circuit elements havinglimited damping. This works against the generation of short pulses since the low damped circuits tend to generate persistent oscillations, and, furthermore, the oscillations build up slowly.

In the present invention, I propose to provide means for not only generating a short pulse but, in addition, I propose to sharpen and shorten the pulse by means of an oscillator-power amplifier system which will now be described.

Referring to Fig. 1, a multi-vibrator l is conneoted through a transformer 3 to a vacuum tube amplifier 5, the primary 1 of the transformer 3 may be shielded from the secondary 9 by an electrostatic shield II. The secondary 9 is preferably of low inductance and, together with the input capacity of the amplifier 5, may be tuned to resonate at the period of the applied pulse. The grid electrode 13 of the amplifier 5 is biased negatively with respect to the cathode [5 by means of a biasing battery IT.

The anode of the amplifier 5, is connected through an inductor l9 to the positive terminals of a B battery 2!. The negative terminal of the batter 2| is connected to the positive terminal of the biasing battery H, the cathode l5 .and ground. The inductor i9 is coupled through a blocking capacitor 23 to the grid 25 of a second amplifier 21. The grid 25 is biased negatively with respect to the cathode 29 by a grid resistor 3l Which is connected to the negative terminal of the biasing battery IT. The natural period of the inductor i9 and its associated capacitie is preferably of the order of, or less than, the natural period ofthe pulse applied to it. The inductor l9 may be shunted by a potentiometer 33. The anode circuit of the second amplifier 21 is connected through an inductor to the positive terminal of the B battery 2|. The inductor 35 may be shunted bya potentiometer 31. The inductor 35 is preferably adjusted so that its natural period is of the order of, or less than, the natural period of the applied pulse.

A master osci1lator39 i connected to a power amplifier 4| which is suitably coupled to an antenna .43. Theimaster oscillator is keyed by a connection 45 to the potentiometer 33. The power amplifier 4| is keyed by a connection 4! to the potentiometer 31.

In the operation of the device, the amplifier and keying net'work generates pulses which are shown in Fig. 2. The characteristic output of the multi-vibrator is represented by the saw-tooth wave 49. The pulses 5| are derived from the charging circuit in the multi-vibrator. These pulses 5| appear in the secondary 9 as positive pulses 53. The positive pulses applied to the first amplifier are difierentiated, in the mathematical sense, to create the highly damped wave train 55. It will be noted that the period of the first come plete oscillation of the damped wave train is of the order of the. period of the applied positive pulse 53. The positive pulse of the highly damped wave train 55, or a portion thereof, is applied to the second amplifier 2'! to thereby generate a second highly damped wave train 57 which is again. due to the differentiating action of the inductor 35. The period of the positive pulse in the first wave train may be represented by t. while the period of the positive pulse in the second wave train may be represented by t/lt, and

in which 7c is preferably of the order of two or more.

The operation of the entire system is represented in Fig. 3 in which the graphs of the wave trains areenlarged to show more clearly the relative-timing of the several pulses. The first keying impulse 59 is used to start the master oscillator which generates a pulse 61 of radio frequency energy. This pulse of radio frequenc energy is applied to the power amplifier H. In order that the pulses derived from the power amplifier may be further shortened, the second keying pulse 83 is employed to key the power amplifier. It should be understood that the bias voltages may be so adjusted that all or any portion of the second keying impulse may be used whereby the duration of the impulse 65 in the power amplifier may be made to coincide with any desired portion of the oscillato pulse.

This invention has been described as a pulse generating device or method inwhich pulses are amplified and at the same time shortened. The longer pulses are used to key the master oscillator and the shorter pulses are 0 arranged to key the power amplifier during the desired portlon of the oscillator keying period. The resultant efiect is to diminish the pulse length in the power amplifier and at the same time permit the master oscillator to attain its full power output. It will be observed that the system works automatically without the application of any mechanical keying means. The rate at which the pulses are radiated is determined by the number of pulses applied to the multi-vibrator or generated thereby. When used for detecting ob-' sta'cles or measuring altitude, the pulse rate is determined by the greatest distance to be observed, while the pulse length 'is a function of the shortest distance to be measured. While the pulse generator has been shown as employing two stages, it should be understood that any desired number of stages may be employed and the keying may be accomplished by employing connections to any of the stages to thereby regulate the duration of the several pulses.

I claim as my invention.

1. A pulse generator device including, :in combination, a source of rapidly varying currents, means for generating pulse from said cur-rents,

means for amplifyingand shortening said pulses, a master oscillator, means for keying the master oscillator by applying thereto the first mentioned pulses, a power amplifier, means for keying the power amplifier by applying thereto the amplifled and shortened pulses.

2. A pulse generator device including, in combination, a ource of rapidly varying currents, means for generating pulses from said currents, means for amplifying said pulses, mean for further amplifying and shortening said pulses, a master oscillator. means for keying the master oscillator by applying thereto the first mentioned amplified pulses, a power amplifier, means for keying the power amplifier by applying thereto the second mentioned amplified pulses.

3.A pulse generator device including, in combination, a source of rapidly varying currents, means for generating pulses from said currents, means for amplifying and shortening said pulses, means for further amplifying and shortening said pulses, a master oscillator, means for keying the master oscillator by applying thereto the first mentioned amplified pulses, a power amplifier, means for keying'the power' amplifier by applying thereto the second mentioned amplified pulses. I

4. A pulse generator device including, in combination, a source of rapidly varying currents, means for generating pulses from said currents, means including a biased tube for amplifying said pulses, means including a biased tube for further amplifying and shortening said pulses, a master oscillator, means for keying the master oscillator by applying thereto the first mentioned amplified pulses, a power amplifier, means for keying the power amplifier by applying thereto the second mentioned amplified pulses.

-5. A pulse generator device including, in combination, a source of rapidly varying currents, means for generating pulses from said currents, means including a biased tube for amplifying and shortening said pulses, means for further amplifying and shortening said pulses, a master oscillator, means for keying the master oscillator by applying thereto the first mentioned amplified pulses, a power amplifier, and means for keying the power amplifier by applying thereto the second mentioned amplified pulses.

6. An obstacle detecting system including; in combination, a master oscillator and a power amplifier to be keyed by pulses of respectively shorter duration, a source of discrete pulses, means for converting said discrete pulses into a first source of highly damped wave trains, means for applying the first positive pulses of said wave trains to key said oscillator, means including said first named means for creating a second source of highly damped wave trains, and a power amplifier connected to said oscillator means f or applying the first positive pulse of said second source of highly damped wave trains to key said power amplifier. I

7. A keying device including, in combination, a keying circuit, a source of current pulses, means for transforming said .pulses into a series of wave trains, means for highly damping said wave trains, said trains including negatively phased pulses and positively phased pulses, means for amplifying the-firstof each .of said positively phased pulses, an oscillator, means for applying said positive pulses to key said oscillator, means responsive to .said positively phased pulses for creating a second series of wave trains, means for highly damping said second series of wave trains, said second series of wave trains including negatively phased pulses and positively phased pulses, a power amplifier, means for applying the first of each of the last mentioned positively phased pulses to key said power amplifier.

8. The method of establishing pulses of radio frequency energy which includes generating pulses of current, generating radio frequency oscillations, controlling the duration of said oscillations as a function of said pulses, amplifying said pulses, amplifying said controlled radio frequency oscillations, and limiting the duration of said amplification of controlled oscillations as a function of said amplified pulses.

9. The method of establishing pulsesof radio frequency energy which includes generating pulses of current, generating radio frequency oscillations, controlling the duration of said oscillations as a function of said pulses, amplifying and shortening said pulses, amplifying said controlled radio frequency oscillations, and limiting the duration of said amplification of controlled oscillations as a function of said amplified pulses.

10. The method of establishing pulses of radio frequency energy which includes generating pulses of current, amplifying and shortening said pulses, generating radio frequency oscillations, controlling the duration of said oscillations as a function of said amplified and shortened pulses, further amplifying and shortening said pulses,

amplifying said controlled radio frequency oscillations, and limiting the duration of said amplification of controlled oscillations as a function of said amplified pulses last mentioned.

11. The method of generating sharply defined pulses of radio frequency energy which comprises generating saw-tooth oscillations, converting said saw-tooth oscillations into discrete pulses, transforming said discrete pulses into wave trains including highly damped negatively and positively phased pulses, generating radio frequency oscillations, regulating the duration of said oscillations by applying to them said positively phased pulses, amplifying said positively phased pulses, amplifying said radio frequency oscillations and controlling the duration of said amplification by applying thereto the amplified positively phased pulses.

12. The method of establishing pulses of radio frequency energy which includes generating highly damped wave trains, generating radio frequency oscillations, controlling the duration of said oscillations as a function of the first positive pulse of each of aid wave trains, amplifying said positive pulses to form second highly damped Wave trains, amplifying said radio frequency 08- cillations, and controlling the duration of the last mentioned amplification by applying the first positive pulse of each of the second series of highly damped wave trains.

IRVING WOLFF. 

